Medium: 0.3 M phosphate buffer, pH 6.0 (prepared by dissolving 816.5 g of monobasic potassium phosphate and 48 g of sodium hydroxide in about 4 L of water, mixing, and diluting with water to 20 L. Adjust with either concentrated phosphoric acid or 1 N sodium hydroxide to a pH of 6.0 ± 0.05); 900 mL.

Apparatus 2: 75 rpm.

Times: 30, 45, 60, and 120 minutes.

Standard solutions— Prepare five solutions of USP Clarithromycin RS dissolved in acetonitrile and diluted in Medium, with known concentrations over the range of about 60 to 600 µg per mL.

Test solution— Use portions of the solution under test passed through a 35-µm polyethylene filter.

Chromatographic system— Proceed as directed in the Assay.

Procedure— Separately inject equal volumes (about 50 µL) of the five Standard solutions and the Test solution into the chromatograph, and measure the responses for the major peaks. Perform a linear regression analysis to generate a standard curve using the peak area of each Standard solution versus its concentration. Determine the amount of clarithromycin (C38H69NO13) dissolved at each specified time interval, using the peak area of each Test solution and the linear regression statistics for the Standard solutions.

Tolerances— The percentages of the labeled amounts of clarithromycin (C38H69NO13) dissolved at the times specified conform to the following Acceptance Table.

Medium: 0.05 M phosphate buffer, pH 6.8 containing 0.5% of sodium lauryl sulfate; 900 mL, degassed by sonication and vacuum.

Apparatus 1: 100 rpm.

Times: 2, 12, and 24 hours.

0.067 M Phosphate buffer, pH 2.5— Dissolve 9.2 g of monobasic sodium phosphate monohydrate in about 800 mL of water. Adjust with phosphoric acid to a pH of 2.5. Dilute with water to 1000 mL.

Mobile phase— Prepare a filtered and degassed mixture of methanol and 0.067 M Phosphate buffer, pH 2.5 (65:35). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Transfer about 56 mg of USP Clarithromycin RS, accurately weighed, to a 100-mL volumetric flask. Add 10 mL of methanol, and sonicate to dissolve. Dilute with Medium to volume.

Test solution— Centrifuge the solution under test at 2500 rpm for 10 minutes.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1.0 mL per minute. The column temperature is maintained at 50. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0; the column efficiency is not less than 2000; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 5 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Determine the amount, in percentage, of clarithromycin dissolved by the formula: in which CU is the concentration, in mg per mL, of clarithromycin in the sample at each time point; rU and rS are the peak responses obtained from the Test solution and the Standard solution, respectively; and CS is the concentration, in mg per mL, of clarithromycin in the Standard solution.

Tolerances— The percentages of the labeled amounts of clarithromycin (C38H69NO13) dissolved at the times specified conform to Acceptance Table 2.

Medium: acetate buffer, pH 4.75 (prepared by dissolving 3.59 g of sodium acetate trihydrate and 11.0 mL of 2 N acetic acid in 1000 mL of water, and adjusting with 2 N acetic acid to a pH of 4.75); 1000 mL.

Apparatus 1: 10 mesh; 50 rpm.

Times: 1, 2, 4, 8, and 12 hours.

0.067 M Phosphate buffer— Dissolve 9.12 g of monobasic potassium phosphate in 1000 mL of water, and mix.

Mobile phase— Prepare a filtered and degassed mixture of methanol and 0.067 M Phosphate buffer (65:35), mix, and adjust with phosphoric acid to a pH of 4.0. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard stock solution— Dissolve quantitatively an accurately weighed quantity of USP Clarithromycin RS in methanol, shaking and sonicating if necessary to ensure dissolution, to obtain a stock solution having a known concentration of about 625 µg of clarithromycin per mL, taking into account the stated potency, in µg per mg, of USP Clarithromycin RS.

Standard solution— Transfer 10.0 mL of the Standard stock solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix. This solution contains about 125 µg of clarithromycin per mL.

System suitability solution— Dissolve quantitatively an accurately weighed quantity of USP Clarithromycin Related Compound A RS in methanol to obtain a solution containing about 625 µg of clarithromycin related compound A per mL. Transfer 10 mL of this solution and 10 mL of the Standard stock solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Test solution— Withdraw 10-mL of the solution under test. Transfer 3 mL to a 25-mL volumetric flask, and dilute with Mobile phase to volume. Pass portions of this dilution through a 0.45-µm filter. Replace 10 mL of Medium in each vessel.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1.0 mL per minute. The column temperature is maintained at 50. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.75 for clarithromycin and 1.0 for clarithromycin related compound A; and the resolution, R, between clarithromycin and clarithromycin related compound A is not less than 2.0. Chromatograph the Standard solution, and record the responses as directed for Procedure: the column efficiency, determined from the clarithromycin peak, is not less than 750 theoretical plates; the tailing factor is not less than 0.9 and not more than 2; and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Determine the amount, in percentage, of clarithromycin (C38H69NO13) dissolved by the formula: in which CU is the concentration, in mg per mL, of clarithromycin in the sample at each time point; rU and rS are the peak responses obtained from the Test solution and the Standard solution, respectively; CS is the concentration, in mg per mL, of clarithromycin in the Standard solution; 100 is the conversion factor to percentage; and LC is the Tablet label claim, in mg.

Tolerances— The percentages of the labeled amount of clarithromycin (C38H69NO13) dissolved at the times specified conform to Acceptance Table 2.

Determine the percentages of the labeled amount of clarithromycin (C38H69NO13) dissolved by employing the following method.

Time (hours)	Amount dissolved
2	not more than 25%
4	between 20% and 40%
8	between 45% and 75%
12	not less than 80%

(50/3)(C/N)(rU / rS)